Light projector



L. BELL. LIG'HT PROJECTOR; APPLICATION FILED Ffa.v19.x9;9.

atent Dec. E2

9 192i? 2 SHEETS-SHEET l.

www

Lal-1s.. UGHT PROjECTOR.

APPLICATION FILED FEB. 19. l9l9. Lw; 'mmm m im, w22..

2 sHEETsfsHEET 2.

i Lentement., oir inns@ 1 nel rl .y y meer rnoancron.

ap'piieiuoiiniea reti-nary 1e,` me. serial in). 277,957.

To aZZ 'LU/icm 'it may concern: v

Be it known' the-t I; Louis BELL, a citizen ofthe United States,resid-inget West New ton, county of Middlesex, Commonwealth ofMassachusetts, have invented certain new and useful improvements inLight yrojectors7 of which the following is a specification. y

The projection of a beam ot' light is customarily accomplished by theuse of lenses with the light approximately in the focus, or by mirrors,generally paraboloidel, although .spherical and other 'forms have beenoccasionally employed. Such projection has its limitations both inperformance and in production.

lt is the object of my present invention to provide projf-:ctorsl oi. e.highly increased range in variety of performance and also of formscapable of accurate commercial production.

lt is not infrequently desirable to pro ject a boem of other thancircular cross sec tion, as in such lights desiened to light up objectsover e considerable horizontal angle, for the illumination of signs, torlightingF buildings, and for use as automobile head'- ligi'hts, :forlighting up a considerable Width of roadway Without at the seine timegiving a beam of similar Vertical dimension. To meet these ends in myprojecting system. l employ a reflecting surface 01' toroidal shape.

The simplest form of toroidal surface is a portion of a surfacegenerated by the revolution of a circle about a fixed axis lying Withoutits center, in the same plane. yThe section and plan oit a tore soconstituted is circular, as shown in Figs. 9 and l0.

ln cases Ywhere notably unsymrnetrical distribution of the ligght isdesired, l prefer to use a toroidal surface derived :trom thegeneralized tore. in which any regular plane curve is rotated about afixed axis lying in the saine plane. on a radius rector not necessarilyconstant but which muy vary as the polar coordinate oi any desired planecurve. For example, Figs. ll and 1Q. show a tore of which the section isen apioid and .the plan is likewise un opioid. Sniniilarly from any ofthe family et' Cartesian oval tores may be derived whether elilre inplan or sec` tion or not. rlhe circular tore is merely an intermediate'form of the family.

An ordinary toroidel surface derived from the circular toroid givesfrom- :1 symmetrically placed source o't' light a symmetricallydistributed beam. vsymmetry can be obtained by decenteringthe source oflight with respect to the surface ashereinafter described, but when itis desirable to obtain wide variations troni .a symmetrically uniformdistribution, such for example as are required to give approximatelyuniform illumination over a surface not symmetrically disposed withrespect to the projecting' system, the use ot' e toroidel surfacederived from e. non-circular toroid becomes desirable. For example.y inflood llighting the 'facade of a building from a point near the groundlevel, uniformity oi illumination is greatly facilitated by using;n atoroidal reflector of the non-circular type which ot' itself wouldproduce a distribution very far from uniform..

My invention lends itself not only to re fleeting?Y projectors.v butalso to projectors ot combined reflecting and refreciting function suchas the liliangin mirror.

As illustrative of the 'forms which li may employ in the embodiment ofmy invention, l here selected several characteristic surfaces ofrelieotion for the purpose of illustration, features thereof beingindicated byrefer ence characters. ln the drawings:

Fig. l is a fece view of a mirror-in accordance with my invention. l f

Fig. 2 section on the axis 2-2 of Fig. l,

Fig. 3 a section on the axis 3-'3 ot Fig. i.

Fig. 3a is a correspondinfhT section to that shown in Fig. 3 of amodification in which the toroid ot the rear face is laterally displacedn'ith reference to the front ieee.

Fig. et a diagrammatic View indicating the Alateral spread of aprojected light beam 'from a mirror in accordance with my invention.

Fig. 5 substantial yerticel symmetry of the sides of such beam.

my mirror.

Small variations from is a similar View indicating the'unieron;razessaonusnrrs,nssieiion fro iinufann'n. sourire. Y neueren,onunrvron, ernssacnosn'rrs..

' as shown in Figs. l, 2 and 3.

Fig. i' a section on the line 7 7, FigI 6.

Fig. 8 a section on the line 8 8, F 1g. 6.

Figs. 9 to l2 inclusive, are in order, plans and sections each of acircular tore and an apioidal tore, respectively.

Fig. 13 is a plan of a torio projector of the apioidal type.

Fig. 14 a section on the line lli- 14, Fig. 13 andY Fig. 15 a verticalsection on the line ils-15, Fig. la

ln the forms shown l have indicated a reA `ilector adapted. to be usedwith a source of light such as the incandescent bulb as beingmostpractieal for ordinary purposes. ASuch a source of light While notexactly punctiform is suiliciently small with reference to thereflecting surface to give results' su'lliciently approximate for mostpurposes of light projection. lVhile in the case of parabolic Vorspherical mirrors, there is a relatively small focal point correspondingroughly to a conjugate focus somewhere along the axis of symmetry, inthese toroidal mirrors the source of light is not conjugate to any pointWhatever, but cnlyto a surface determined by the form of the toroid.

l prefer for the purpose of more accurate projection to form myreliectin surface as the back B of a mirror of the h angin type, Thissurface l formas a toroid having a curvature ab on the line of verticalVsection 2 2 Aof Fig. l, as shown in Fig. 2, and a curvature c aon theline of transverse section 3 3 of Fig. l

as shown in Fig. 3.

Similarly the front or retreating surface A of this embodiment of myinvention is symmetrically toroidal with the rear or reliectingsurface Bhaving a curvature a2, on the line of vertical section 2 2 as shown inFig. 2, and a curvature c2, d2, on the line of transverse section 3 3,as shown in Fig. 2. There is th 1s a symmetrical correction of theaberrations similar to that in the ordinaryv spherical form of Manginmirror.

In case of mirrors of relatively longer radius approximate correction ofthe aberration is.obtainable by a spherical anterior or refractingsurface of radius of a length intermediate that of the radius of c2, b2,and c2. d2.

lThese mirrors are furnished with a ccntral aperture E for the receptionof the socket of an incandescent lamp L. As shown in Fig. 5, thefilament of this lamp L is approximately in focus for the surface ofvertical axis of the surface B taking into account the refractive eifectof the anterior surface A. lt therefore causes so farA as the verticalaxis 'is concerned a substantially parallel beam (L, "l f, d, asindicated in Fig. 5. 1

in the horizontal axis rays from the source of light L incident upon thereflecting surface B, at the points c, d and correspond ingly upon thesepoints, taking into account the refractions on the anterior surface Athe resulting beam c, fr cl, k is spread in the horizontal direction asshown in Fig. Ll.

The result of this distribution therefore is a beam as a whole of ovalsection, covering much greater width than height. or much greater heightthan width if turned ninety degrees. lt may therefore in the firstposition spread laterally to considerable` area, or in the secondposition spread vertically tc cover towers, steeples and the like.

ln the use of such a light projecting system, the toroidal curves of myconstruction are easily ground accurately by automatic machinery, muchmore easily than paraboloidal orother surfaces varying from the sphereso that the resulting mirror is substantially easy to produce as theordinary spherical Mangin mirror.

. ln the somewhat modified form of my iny vention shown in Figs. 6 to 8,I have indicated an embodiment of my invention in a single surface typeof reflector shown in the face view in Fig. 6. The surface of thisreflector S which maybe a metallic reflector or reflector of any Wellknown type, is a toroidal surface having a vertical curvature e,indicated in the section, taken on the line 7 7 of Fig. 6. Thiscurvature of axis at right angles thereto is as appears in the sectionvin Fig. 8, along the line i `which is the section on line 8 8 of Fig.6.

lVhere it is desirable to pitch thelight downward with such a projectoras is shown in Figs. 6 to 8, this is easily accomplished withoutmaterial disturbance of the func. tions of the reflecting system hy aslight deccutering of the source of the light upwards from thediametrical center of the reflector.

As shown in Fig. 6, where the lamp opening E has its center slightlyabove the intersection of the two optical axes of symmetry. The resultis similar to the performance of the projector shown in Fig, l, wherethe eenter of the perforation is in the center X of the mirror face asa. whole, while the curvature of the rear reflecting toroidatlsurface Bis displaceddownwardly so' that its horizontal axis passes through Ybelow the mirror center I In such construction, the oval beam of theprojected light, c, oil-7), (l, dips slightly downward relative to thehorizontal as sho-wn in Fig. 5.v

For concurrent lateral symmetry of distribution the source of light mayhe shifted from the optical. center laterally as Well as vertically,either by actually displacing the lamp itself relative to the toroid, orin the ii'l'angin type hy displacing the rear toroidal.

curvature with respect to the source of light. so as to bring tl"`y'tntersectmn of the planes of the symmetry .-f the concurrent cylin.riotios o the iosirofi point of lisp-imo@ as moro yim-lusive. Si is opion View oit' 2i circular in il I 11a-Vo indicated a tom of pioidaiplan sind also apioidol section as mdloutedn:

iig. l2. By considering the 'oiationship of these two types of toro therelation of my projector shown in Fi 13 to i5 to the,

forms irst described wi l. be;4 apparent. /he projector shown in plainin Fig, 3.3 has' o veiicai section as appems in Fig. l5 i'opro senting aculcifwturo g1-PQ while a cross soo'- tion as on the line 14C-141- i;has a oirvw ture @'L iin practice the general type of atom to heselected Wiii oo appuient to those, skiiiod in. the im; from the above;disclosures. in this way any desii'od distribution of illumination overany surface from any point 01 points at which projectors maj/,beinsmiied, may

be had bw ein lo in@ iro'ootors of sur'i'aoa J P D P in aocoidanoe withmy invention.

Wha@ therefore daim :md desire to sooui' .Lowers Fatemi, iS: y

a toroidal siii/@foci hi'ickE and ifiaving 'oil Speotiyeiy withiho.,axes of the vom@ mzmid but respectively oi" shower radius of mimi-1,tufo, such radii of ourvaufe boing iojpoiM 4wtimed to the wim-@tivoindex of the @mio parent material so as io effect :ippi'oizimooox'recbioto of the abdeiio'tion.

3. mirror of "iionspalont material hav ing a, toioidol i'oloC-ixing yoursurface :md a toroidai fiom i'efracting surface of i'osspecgiveiypai'aiioi with the of h@ 'rom' tooid and of ouimtuies modiifyiiig nheiight distribution dotominefi by the, new roeoting surface., f

4E. iight prog'eo'ning roiootoi' of trims paient mata-iol having sitoroiiai rom. surface of' ieeotiozi sind a oroidoi ioht surface ofrofiaotifonz oiiid tooidapi surfaces ho ing of curm'tros inerioiatedeach to suppioment tho ahor tix/'e 'tendency of the ohoi.

5. A. iight projo/ting roimbor of minspment motorini having a tooidolremoto'- a/ce of i'eeotion alud a, front 'rofiaoing smaioo ofFo'v'loiutions whose axis is noli-coin aident 'Wiih either of tho mos o'the zoioiioi reooting surface. I in testimony whore-off )i aix mySigimaum .in presanco of two "Wimoses,

Gmomm G., Lownmm

